1. Field of the Invention
This invention relates to coating equipment using an extrusion type coating head for uniformly applying a coating fluid to the surface of a continuously running belt-like support, and more particularly to extrusion type coating equipment for uniformly applying a coating fluid to a support surface in a non-pressurized condition when the coating fluid is coated to the support surface from a slot.
2. Description of the Related Art
Hitherto, a step of applying a desired coating fluid to the surface of a flexible support has been executed in a manufacturing process of photo-sensitive material, magnetic recording media, etc. Coating fluids containing various fluid compositions are available according to their applications. For example, coating fluids of photo-sensitive emulsion coats, undercoats, protective coats, back coats, etc., are available for photo-sensitive material and magnetic coats, undercoats, protective coats, lubricant coats, etc., are available for magnetic recording media. The coating fluids are aqueous solutions, organic solvent solutions, etc., containing essential components, binders, and various admixtures as required.
Hitherto, various application methods, such as a roll coat method, a gravure coat method, a roll coat plus doctor method, extrusion type application method, and slide coat method, have been used as methods of applying such coating fluids to the flexible support surface. In recent years, an application method using an extrusion type coating head has been often used for applying a magnetic coating fluid.
A typical method using an extrusion type coating head is, as well known, a method of applying a thin and uniform coating of fluid extruded from the slot end to the surface of a continuously running flexible support with the coating head disposed between a pair of run guide means spaced at a given distance apart at a predetermined location on which the flexible support is placed.
Coating equipment using the extrusion type coating head is disclosed, for example, in Japanese Patent Laid-Open No.Sho 63-20069. As shown in JPA1069, the coating equipment comprises a coating head disposed between support guide means (rollers), the coating head comprising a front edge positioned upstream with respect to the running direction of a support, a back edge positioned downstream sloped in the direction opposite to the support so that the top of the back edge recedes from the top of the front edge, a coating fluid spouting slot defined by both the edges, and coating width regulation plates on both sides of the slot for regulating the width of a coating fluid spouted from the slot tip. In the application step using the coating equipment, part of a low-viscosity fluid previously applied to the support is scraped out by the front edge in order to completely exclude air accompanying the support, so that the coating fluid spouted out from the slot tip can be applied to the support surface in a non-pressurized condition.
However, if an attempt is made to apply a uniformly thick coating of coating fluid to the running support surface with the non-pressurized extrusion type coating head, a phenomenon called "film cut" occurs on both side ends of the coat (left and right ends in the direction perpendicular to the running direction of the support). The film cut is described in conjunction with FIG. 12 which is a sectional view of a part cut along the slot of the coating head. The running direction of the support is a direction perpendicular to the plane of the paper and directed from downward to upward. As shown in FIG. 12, coating fluid 36 is continuously supplied from the bottom in the figure through the slot to the surface of the support 30 to which precoat 35 has already been applied.
At this time, the front of the coating fluid 36 is liquid-sealed by the precoat 35, but an opening is made between the upper edges of coating width regulation plates 7 and the support 30 on both left and right ends. Air pressure entering through the part causes film cut 38 to develop between the coating fluid 36 and the precoat 35. In the application method in which large application pressure is not produced when the coating fluid 36 is applied, the film cut 38 appears as a thin coat is applied at high speed.
The coating width regulation plates 7 may be brought nearer to the support 30 for preventing air from entering. However, as the upper edges of the coating width regulation plates 7 are brought near the support 30, the risk of the coating width regulation plates 7 contacting the support and damaging it is increased. Particularly when the coating width regulation plates 7 are made of metal, the support is damaged severely.